The objective of this proposal is to develop a tool for determining microvascular flow distribution from images of myocardium. This involves quantifying the spatial distribution of blood flow in arteriolar trees with lumen diameters in the range of 10 - 50 m. High resolution micro-CT imaging will provide accurate 3D geometrical mapping of the microvascular architecture for a computational determination of the flow distribution. This gold standard will be used to calibrate estimates of sub-resolution regional blood flow distributions obtained by nested-region-of-interest (nROI) analysis of clinical MSCT images of myocardial perfusion. The significance of this proposal is that it will make it possible to probe deeper and more accurately into the mechanisms of microcirculatory disease processes in the myocardium and elsewhere (e.g., in diabetes mellitus, hypertension, and atherosclerosis). There is currently no imaging methodology for assessing quantitatively the state of microvasculature in humans with sufficient resolution as to allow the computation of flow distribution at the level of individual microvessels. The proposed method will provide a new tool for exploring novel diagnostic and treatment methods. The innovation in this proposal is that it will provide for the first time a 3D mapping of sub-resolution microvascular flow distribution with MSCT imaging methodology validated with micro-CT. AIM I - Generation of Whole-body and Micro-CT Image Data - Ia: Using pigs, generate an MSCT image sequence while the contrast bolus passes through the coronary circulation. Then, repeat this procedure while the LAD coronary artery is infused with adenosine. Next, inject 15 m radiopaque microspheres (Ag impregnated) into the left atrium during resting flow conditions and then Au impregnated microspheres during the selected adenosine delivery rates. Ib: The heart will be removed and the LAD injected with Microfil. Several 1 cm3 muscle samples will be removed from the LAD perfusion territory. Each specimen will be scanned at (4 m)3 voxel resolution. AIM II - Analysis of Convective Flow Distribution within the Microvasculature - IIa: The 3D micro-CT images of the specimens will be segmented so that our tree analysis program can provide the vascular lumen inter-branch segment diameter, length and branching angle and branch hierarchy in order to compute a hemodynamically-based flow distribution. IIb: The microspheres will be digitally isolated so that their location and density can be used to provide a microsphere-based flow distribution. IIc: The microsphere and hemodynamically based flow distributions will be compared and any differences will be accounted for to establish the true flow distribution. AIM III - Analysis of Spatial Heterogeneity of Myocardial Perfusion Within the Same Myocardial Regions -The MSCT images of the myocardium will be subjected to nROI analysis and used to compute the spatial distribution of intramyocardial blood volume and flow and the results will be calibrated by the distribution of flow and intraluminal blood volume as derived from the micro-CT results in IIb, c.